The organic light emitting diode (OLED) is one of the hotspots in the panel display research field nowadays, as a current type light emitting device, it has been increasingly applied in the high performance display field due to its characteristics of self-luminous, quick response, wide visual angle and capable of being fabricated on a flexible substrate. At present, the OLED has begun to replace the conventional liquid crystal display (LCD) in the display fields of mobile phones, PDA, digital camera and the like. The pixel driving circuit design is the core technical content of the OLED display, which has important research significance. Different from the thin film transistor (TFT)-LCD which makes use of a stable voltage to control the luminance, the OLED belongs to current driving, which requires stable current to control luminescence. Due to technological process and device aging, in the original 2T1C driving circuit (including two thin film transistors and one capacitor), the threshold voltages of respective pixel points for driving the TFT are nonuniform, thus it results in variation of the current that flows through each pixel point OLED and makes the display luminance nonuniform, thereby influencing the display effect of the whole image.